Prompt — GPU flow field

Build a single self-contained HTML file called index.html containing a three.js GPU particle flow-field simulation. No build step, no bundler, no local dependencies — load three.js from a CDN with an ES module import map.

Simulation requirements

• 200,000 particles minimum, rendered as a single THREE.Points object with a custom ShaderMaterial. One draw call.
• Particle motion is driven by a curl-noise flow field computed in GLSL, not on the CPU. Write the noise function yourself in the shader — simplex or value noise is fine, but it must be in the shader source, not imported.
• Curl noise means: sample a potential field and take its curl, so the resulting velocity field is divergence-free and the particles swirl instead of clumping into sinks. Compute the curl by finite differences of the noise.
• Particles must have a finite lifetime. When a particle dies it respawns at a new position. Handle lifetime and respawn on the GPU using the vertex shader and a per-particle seed attribute, driven by a single uTime uniform.
• Particle colour varies with velocity magnitude, using a palette defined in the fragment shader. Faster particles should read as hotter.
• Additive blending, depth write disabled, so dense regions bloom naturally.

Visual requirements

• Particles rendered as soft round points, not hard squares. Discard fragments outside the point radius and fade toward the edge.
• Dark background with a subtle vignette or gradient — not flat black.
• The camera slowly orbits the field on its own so the three-dimensional structure is visible without the user touching anything.
• Maintain interactive framerate. Say in a comment what you did to keep it fast.

Interaction requirements

• Mouse movement distorts the flow field near the cursor position, pushing particles away. Pass the cursor in as a uniform.
• Keyboard or on-screen controls for: noise scale, flow speed, particle lifetime.
• An FPS counter, computed yourself rather than from a library.

Constraints

• One file. Everything inline: HTML, CSS, JavaScript, GLSL as template strings.
• Must run correctly when opened directly in a browser.
• No external assets — no texture files, no model files, no images. The particle sprite must be generated procedurally in the fragment shader.
• Handle window resize correctly, including device pixel ratio.
• Do not use deprecated three.js APIs; target a current version and say which version you targeted in a comment at the top.

Output the complete file. Do not abbreviate any section or leave placeholder comments like "rest of the code here".